Method of producing magnesium



June 15, 1965 D. M. PEPLINSKI 3,189,439

METHOD OF PRODUCING MAGNESIUM Filed May 6, 1963 2 Sheets-Sheet 1 /M Q 2am LATENT AGENT June 15, 1965 D. M. PEPLINSKI 3,189,439

' umuon OF PRODUCING MAGNESIUM Filed llay 6, 1963 2 Sheets-Sheet 2 BATEN'L AGENT United States Patent ice 3,189,439 Patented June 15, 1965 3,189,439 METHGD F PRODUCING MAGNESIUM Desmond M. Peplinski, Haley, Ontario, Canada, assignor to Dominion Magnesium Limited, Toronto, Ontario, Canada Filed May 6, 1963, Ser. No. 273,316 2 Claims. (Cl. 75-67) This invention relates to an improved method of producing magnesium.

In the production of magnesium by, for instance, the Pidgeon procedure, there are provided a plurality of retorts each having a reducing portion disposed within a furnace and containing a charge of magnesia and a reducing agent and a condensing portion without the furnace. Means are provided for maintaining a reduced pressure in the retorts and comprises a vacuum line connected to each condenser portion. Condensation of magnesium vapor produced in the reducing portion of each retort occurs in the cooled condenser which is usually provided with a removable liner upon which the magnesium vapors condense.

During the condensing cycle, the flow of magnesium vapour requiring to be condensed builds up to a peak rate and then tapers ofi as the reduction reaction nears completion. The upper limit of this peak condensation rate of vapour flow is contingent on the size of the reduction charge, the rate of heat input to the charge and charge reactivity which is subject to change because of uncontrollable operating variables. The condenser capacity is regulated by its ability to accommodate the peak flow of magnesium vapour and any variations that might occur in this peak for reasons already mentioned. Failure to provide the necessary condensing capacity to handle these peak requirements results in metal condensing in liquid form which can run back into the hot zone thereby causing refiuxing, a condition known commercially as hot crowns.

It is an object of this invention to provide, in the production of magnesium, a method of increasing the handling capacity of the condenser by restricting vapour flow and/ or improving heat dissipation efficiency of the condenser during peak condensing period to permit the accommodation of larger reduction charges and reduce the frequency of hot crown occurrences.

The invention will be described with reference to the accompanying drawings, in which FIGURE 1 is a diagrammatic layout of a conventional system operable in accordance with the invention, and

FIGURE 2 is a diagrammatic layout of a modified type of system in accordance with the invention.

Referring to FIGURE 1, retorts each have a reducing portion 11 within a furnace 12 and a condenser section 13 outside the furnace. Means for maintaining reduced pressure in the retorts comprises an individual group retort header 14 which is connected by a line 15 with valve 16 to each retort. Header 14 is connected to a main pull down vacuum header 17 by a pipe 1% with valve 19 and to a main holding vacuum header 20 by a pipe 21 with valve 22. The main pull down and holding vacuum headers are connected to vacuum pumps 23 and 24, respectively.

In conventional operation, pressure in the system is initially reduced from atmospheric pressure by mean of the pull down pump or pumps 23 and the vacuum maintaincd at desired level by switching from pump 23 to the vacuum holding pump 24-.

In accordance with a broad aspect of the invention, just before the peak distillation rate is achieved, i.e., when the temperature of the condenser approaches the melting point of magnesium valve 22 is also closed to disconnect the retort condenser assembly from the vacuum pumps. As heat is transferred to each condenser by magnesium vapour its temperature rises and the temperature of the condenser can be taken as an indicator of the rate of condensation. It has been observed that the temperature of the condenser is reduced by about 50 C. when this operation is performed over a period of about two hours by which time the peak reaction and, therefore, the peak condensing rate is over and the condenser is capable of handling the flow of vapour without any precautionary measure.

Controlling pressure in this manner during the peak condensing period has enabled the condenser capacity to be increased by at least 40% compared to continuous vacuum operation without the temperature of the condensed metal exceeding the melting point.

The modified system illustrated in FIGURE 2 is designed to eliminate any disadvantage that may occur as a result of the fact that, since the retorts are exhausted by the vacuum pump through a manifold system, as indicated, a high leakage in one retort will afiect others connected to the same manifold or header. It will be apparent that, while the rate at which air will leak through a metal retort at 1200 C. is reasonably uniform from one retort to another, there is always the possibility of retorts containing efects or developing defects with age of suflicient extent to result in a fairly high leak rate. Wh le various means may be employed to control the vacuum therein is also in communication with header 20 through pipe 30 having valve 31 therein. Valve 32 is provided in header 29 between the connections of pipes 28 and 30.

In operation, the retorts are initially evacuated by means of the pull down pump 23 and connections which normally takes place over a period of about 60 minutes. The individual group retort header 14 is now switched over to the holding vacuum of pump 24 (valve 32 being open and valves 29 and 31 closed) for about 40 minutes, at which time the peak condensing period normally approaches. Valve 32 is now closed and valves 29 and 31 opened to switch in the by-pass pressure controller, which is connected into the system for, say, about two hours.

With the holding vacuum cut otf, the pressure in the condensers will increase in, say, the range of 500 to 2000 microns which will tend to prevent the capacity of the condensers from being exceeded. This increased pressure will be maintained almost constant by the pressure controller 23 which functions in normal manner.

The condenser cycle may be completed by switching the system back to the main holding vacuum header 20, in which case there is provided an intermediate vacuum main header 33 connected to pipe 28 through pipe 34 and to the individual group retort header 14 through pipe 35 and valve 35. This arrangement provides both controlled pressure for the peak condensing period and maximum vacuum for the remainder of the cycle subsequent to this critical period. Alternatively, intermediate header 33 may be omitted, and the' controlled pressure provided by closing valve 32 and opening valves 31 and 29 to connect through the pressure controller 25 to the main holding vacuum header.

The advantage of employing a pressure controller resides in the controlled pumping action which avoids the variations that would be caused by a leaking retort when no pump is in operation.

Use of the pressure-controlled system produces results maximum recoveries can be handled without having to' increase the size of the condensing equipment; I claim: r

l 1.v A method of producing magnesium in a plurality of retorts each having a reducing zone and a condensing .zone which comprises the steps of heating a charge of magnesia and reducing agent in said reducing zones to cause formation of magnesium vapor from said charge, subjecting said condensing zones to the action of a vac- 1mm pump to reduce the pressure in said retorts and cause fiow'of said magnesium vapor into said condensing zones, :r'naintaining the temperature in said condensing zones less than the melting point of magnesium to cause condensation of said magnesium vapor therein, said condensing zones having a condensing rate cycle comprising an initial build-up period, a peak rate period, and a tapering off period, said temperature'maintaining step including the step of interrupting said vacuum pumping. action during said peak rate period to increase the pressure in said con: 'densing zones and thereby decrease the temperature thereof,

i 2. A method of producing magnesium in a plurality of retorts each having a reducing zone and a condensing zone which comprises the steps of heating a charge of magnesia and reducing agent in said reducing zones to 7 cause formation of magnesium vapor from said charge, initially reducing the pressure in said retorts from atmos pheric to a predetermined level, ubjecting said condensing zones to the actionof a vacuum pump to holdsaid pressure in saidretor'ts at I substantially said, predetermined level, maintaining the temperature in said condensing zones less than the melting point of magnesium to cause condensation of said magnesium vapor therein, said c0n densing zones having a condensing rate cycle, comprising an initial build-up' period, a peak rate period, and a tapers 7 ing. off period, saidttemperaturemaintaining step including' the step of interruptingsaid holding vacuum pump;

action during said peak rate period to increase the f pres,-

sure in said condensing zones andfthereby decrease the" temperature thereof.

References Cited by the Examiner UNITED STATES PATENTS 1 2,330,142 9/43 Pidgeon Q 75-67' 2,330,143 9/43 Pidgeon 75'-'67 2,514,275 7/50 Allen 7567 2,570,232 10/51 2,684,898 7/54 2,971,833 2/61 "3,033,549 5/62 BENJAMIN HENKIN, Primary Examiner. 

1. A METHOD OF PRODUCING MAGNESIUM IN A PLURALITY OF TETORTS EACH HAVING A REDUCING ZONE AND A CONDENSING ZONE WHICH COMPRISES THE STEPS OF HEATING A CHARGE OF MAGNESIA AND REDUCING AGENT IN SAID REDUCING ZONES TO CAUSE FORMATION OF MAGNESIUM VAPOR FROM SAID CHARGE, SUBJECTING SAID CONDENSING ZONES TO THE ACTION OF A VACUUM PUMP TO REDUCE THE PRESSURE IN SAID RETORTS AND CAUSE FLOW OF SAID MAGNESIUM VAPOR INTO SAID CONDENSING ZONES, MAINTAINING THE TEMPERATURE IN SAID CONDENSING ZONES LESS THAN THE MELTING POINT OF MAGNESIUM TO CAUSE CONDENSATION OF SAID MAGNESIUM VAPOR THEREIN, SAID CONDENSING ZONES HAVING A CONDENSING RATE CYCLE COMPRISING AN INITIAL BUILD-UP PERIOD, A PEAK RATE PERIOD, AND A TAPERING OFF PERIOD, SAID TEMPERATURE MAINTAINING STEP INCLUDING THE STEP OF INTERRUPTING SAID VACUUM PUMPING ACTION DURING SAID PEAK RATE PERIOD TO INCREASE THE PRESSURE IN SAID CONDENSING ZONES AND THEREBY DECREASE THE TEMPERATURE THEREOF. 